Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources (e.g., frequency/time resources). Examples of such multiple-access technologies include time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, code division multiple access (CDMA) systems, time division synchronous code division multiple access (TD-SCDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single-carrier frequency division multiple access (SC-FDMA) systems.
These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of a telecommunications standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards preferably using OFDMA on the downlink (DL) and SC-FDMA on the uplink (UL).
There is an increasing need for accurate and reliable location positioning of User Equipments (UEs) within mobile wireless (cellular) communications networks. Some of said methods use entities within the networks to determine a UEs' position. The 3GPP standard identifies a number of standard position determining (positioning) methods including network-assisted Global Navigation Satellites Systems (GNSS) methods; downlink positioning methods; cell ID based methods, and enhanced cell ID based methods. 3GPP also supports hybrid positioning methods utilizing multiple methods from those mentioned above. Of the supported positioning methods, there are two major positioning paradigms in LTE systems, namely client-assisted/network-based positioning methods, and network-based positioning methods. The cell ID based methods and enhanced cell ID based methods are exemplary types of network-based positioning methods.
A typical client-assisted/network-based positioning paradigm is illustrated in FIG. 1A in which a UE 1 receiving a signal 5 measures received signal strength and received signal time difference and communicates 6 these measurements to the base station (BS) or eNB 2 which in turn communicates 7 them to an E-Serving Mobile Location Centre (E-SMLC) 3 which utilizes the measurements to estimate the position (location) of a UE 1 within the mobile network; more particularly a location within the cell of the serving BS/eNB 2. The E-SMLC 3 may be provided in the BS/eNB 2. By way of contrast, a typical network-based positioning paradigm is illustrated in FIG. 1B in which the UE 1 communicates as normal with the BS/eNB 2 and need not specifically report any measurements, and in which the BS/eNB 2 itself measures from a received signal 8 received signal strength and received signal time difference, communicates 7 the measurements to an E-SMLC 3 which utilizes the measurements to estimate the position (location) of a UE 1 within the mobile network. In this latter case, the BS/eNB 2 may also measure the signal angle of arrival for use in the position estimation process.
The client-assisted/network-based positioning paradigm (FIG. 1A) requires user involvement. For example, the user of a mobile device (UE) may need to install an application on the UE 1 or to setup a specific configuration on the UE 1. The network-based positioning paradigm (FIG. 1B) does not require any application to be installed on the UE 1 nor does it require the setup of any specific configuration on the UE 1. The network-based positioning paradigm can detect the location of the UE 1 as long as the UE 1 is powered on. This is useful if the user of the UE 1 loses the UE 1 and would like the mobile network service provider to locate and/or lock the UE 1 remotely.
The accuracy of detecting the location of the UE 1 using the network-based positioning paradigm depends on the accuracy of first signal path of arrival detection, more specifically time of arrival at the BS/eNB 2 of a signal on the first path of arrival, this path comprising the path of minimum propagation distance between the signal transmitting device, e.g. UE 1, and the signal receiver, e.g. BS/eNB 2. However, a multipath effect as illustrated in FIG. 2 may make a first signal path of arrival indistinguishable from other signal paths such as reflected signal paths. This is especially so in an indoor environment. As shown in FIG. 2, a line of sight (LOS) signal path P1 from a UE 1 to a BS/eNB 2 may be interrupted by obstacles 4 such that reflected signals P2, P3 arrive at the BS/eNB 2 by longer propagation paths, but with higher powers. The LOS path P1 and reflected paths P2, P3 comprise a set of multipaths. Consequently, the peak power of the channel impulse response (CIR) of a received signal BS/eNB 2 may not correspond with the first signal path of arrival (LOS path P1) due to the multipath effect. Attempts have been made to address the aforesaid issues.
U.S. Pat. Nos. 8,199,702 and 8,576,782 each discloses baseband recovery in wireless networks, base transceiver stations, and wireless networking devices to minimize the number of timing symbols while at the same time enabling wireless devices to use a relatively low per-symbol sampling rate, so that minimal processing is required to implement the timing recovery. A relatively low number of samples is taken per expected symbol interval during the training sequence. A subset of the samples is selected and processed to determine error signals for each of the samples. The error signals are multiplied by the expected symbol and summed to form an error signal. The error signal is used to adjust the set of samples that will be used and processed in connection with subsequent symbols. The error signal is also used to interpolate between available samples to infinitesimally approach the point of maximum eye opening.
US2004/0170197 discloses a method of synchronizing an Orthogonal Frequency Division Multiplexed (OFDM) IEEE 802.11a data packet at a receiver. The 802.11a data packet has a series of short training sequence (STS) symbols as a preamble. Cross-correlation at the receiver of the STS in the 802.11a packet PLCP preamble with the modified reference STS, that is circular shifted by eight samples, results in a main correlation peak but with reduced pre- and post-lobes. To locate the cross-correlation peak, a running second derivative of the cross-correlation function is performed. Peak selection employs a running comparison of the position and magnitude of all peaks in the intermediate neighbourhood of the local peaks; Following selection of a peak from within the cross-correlation function of the first STS in the PLCP preamble, both the position and magnitude of the first STS is compared to those of the second STS. Based on the two independent calculations, the start of the OFDM frame is estimated.
US2007/0019538 discloses that, for symbol synchronization in a communications system, a plurality of symbols corresponding to a transmitted signal is received, where the plurality of symbols include guard intervals. Peak correlation is obtained using the plurality of received symbols. The second derivative of the peak correlation is obtained, and one or more peaks within a corresponding guard interval are identified from the second derivative. A symbol start time for each received symbol is estimated based on the second derivative of the peak correlation.
U.S. Pat. No. 7,570,707 discloses a method for introducing a delay in either an envelope or a phase signal path of an RF polar transmitter in order to eliminate the delay mismatch between the two paths. For two signal paths, a faster signal may be delayed by a digital processor or a slower signal may be transmitted early so that signals in the two signal paths arrive at a specified circuit node in synchronization. Timing shift may be implemented in either the envelope signal path or the phase signal path and may be used to reduce or increase the timing of a signal path.
US2010/0165915 discloses a wireless network in which one of a base transceiver station and a wireless networking device are configured to implement baseband recovery. The recovery is performed by sampling a received training sequence at a relatively low number of times during each estimated training symbol interval to obtain a relatively low number of samples for each estimated training symbol interval. Then, selecting a contiguous subset of the relatively low number of samples and obtaining a first derivative associated with the subset. The first derivative is multiplied by an expected data symbol to obtain an error signal for the training symbol interval. Accumulating error signals from successive training symbol intervals form an accumulated error signal. A first portion of the accumulated error signal is used to adjust which of the relatively low number of samples are to be included in the contiguous subset in connection with processing a subsequent training symbols. Then, a second portion of the error signal is used to determine a likely position of a location of maximum eye opening to estimate the timing phase from the training sequence.
US2006/0133525 discloses a symbol timing estimation method for use in a communications system in which symbols are successively transmitted in a signal, each symbol comprising a predetermined number of symbol samples, and in which a series of L symbol samples is repeated N symbol samples after its original appearance, where L and N are integers. The method comprises: receiving said signal and processing the symbol samples in the received signal using N and L to obtain a correlation function for the originally-appearing series and the repeated series. It includes producing a basic measure for symbol timing estimation based on the obtained correlation function and producing a second-derivative measure for symbol timing estimation based on a second derivative of the basic measure. Symbol timing is estimated based on the basic and second-derivative measures. The first peak of the second-derivative measure is considered as the rising edge of the first peak of arrival, but, in many cases, this is not the first path of arrival at the receiver.
There is therefore a need to provide an improved means of identifying the first signal path of arrival in a multipath environment in a mobile wireless communications network, i.e. to identify which signal path constitutes the first signal path of arrival at the receiver or is likely to constitute the first signal path of arrival, or to determine a signal arrival time which constitutes the time of arrival at the receiver of a signal at the first signal path or the likely first signal path.